The present disclosure generally relates to methods for producing and purifying 2-hydrocarbyl-3,3-bis(4-hydroxyaryl)phthalimidine monomers (hereinafter sometimes referred to as phenolphthalein derivatives), and polycarbonates as well as other polymers derived utilizing the monomers.
3,3-Bis-(4-hydroxy-phenyl)-3H-isobenzofuran-1-one (hereinafter referred to as phenolphthalein) has been used as an aromatic dihydroxy compound monomer for preparing polycarbonates, which are generally characterized with excellent ductility and high glass transition temperatures. Certain derivatives of phenolphthalein have also been used as aromatic dihydroxy compound monomers to prepare polycarbonate resins as well as polyarylate resins. For example, polycarbonate homopolymers have been prepared by an interfacial polycondensation method using phosgene and (phenolphthalein derivative) monomers such as 3,3-bis(4-hydroxyphenyl)phthalimidine and 2-phenyl-3,3-bis(4-hydroxyphenyl)phthalimidine (hereinafter sometimes referred to as “PPPBP”).
Lin and Pearce (Journal of Polymer Science: Polymer Chemistry Edition, (1981) Vol. 19, pp. 2659–2670) reported the synthesis of PPPBP for preparing polycarbonates and other polymers by refluxing phenolphthalein and aniline hydrochloride in aniline for 6 hours, followed by recrystallization from ethanol. During this reaction, side products are created which, if not removed, can result in PPPBP having an unacceptable purity for use as a monomer or as a comonomer in subsequent polymerization reactions. Furthermore, the impurities in the PPPBP monomer include, for example, trace (parts per million) levels of phenolphthalein or phenolphthalein residues that can undesirably produce discoloration in the polycarbonates and other polymers derived therefrom, thereby affecting the transparency of the polymer product. Coloration is not a desirable attribute for many commercial applications. U.S. Pat. No. 5,344,910 discloses that copolymers of PPPBP were found to have poor melt stability resulting in foamy polymer melts and moldings, and discoloration of the resin during melt processing.
It would therefore be desirable to develop a process for improving the purity of phenolphthalein derivatives such as 2-hydrocarbyl-3,3-bis(4-hydroxyaryl)phthalimidine, which can then be used for producing polycarbonates and other polymers having improved properties, such as lower visual coloration and a higher weight average molecular weight.